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Lecture 22 -- Introduction to Motor Systems -- Martin
Lecture plan
1)
2)
3)
4)
Basic principles of movement control
Sensory control of movement
Components of the motor systems
Descending motor pathways
Hierarchical organization of movements
Reflexes
monosynaptic (knee jerk) and polysynaptic (withdrawal) reflexes
spinal cord
Postural adjustments
feed forward and feedback control
vestibular control of balance
more flexible than simple reflexes, yet more constrained than voluntary movements
brain stem, cerebellum and spinal cord
Voluntary control-prehension
motor equivalence
very context-specific
greater flexibility than afforded by simple sensory representations, whether simple like the stretch
reflex or complex, as for balance
Conclusions:
1. hierarchical organization of neural circuits underlying motor behavior
2. hierarchical organization of sensory-motor control, from stereotypy to flexibility
3. movement depends on internal representations of the sensory world as well as internal
properties (e.g., muscle characteristics; mechanical properties of limbs)
An example of translating sensation into action: Visuo-Motor Control of
Prehension
Prehension=reach and grasp
grasp=preshape hand during reach
Complex planning and execution stages
Motor program specifies:
•movement kinematics (the spatial characteristics of the movement; the angle through which
the joints will move)
•movement dynamics (the forces that are required to move the joints)
“Circuit”
•Vision: where pathway to posterior parietal lobe
•Somatic sensory information (proprioception) integrated here
•Information transmitted to premotor areas, then to primary motor cortex
parallel paths for aiming the reach and preshaping the grasp
CONCLUSION:
•motor systems have selective access to sensory information
•hierarchical and parallel processing
Components of the motor systems
Bottom up view
•Muscle, motor neurons and spinal premotor interneurons
•Descending motor pathways from cortical motor areas and brain stem nuclei
Hierarchical and parallel organization
•Cerebellum and basal ganglia influence function of paths, via thalamus
Conclusion: parallel and hierarchically organized pathways
Descending motor pathways
Origins and spinal terminations
Motor cortexmotor neuron
Motor cortexinterneuronmotor neuron
Motor cortexbrain stem nucleusinterneuronmotor neuron
ETC
Proximal-distal rule of spinal organization
Medio-lateral organization
•medial pathways for posture control
•lateral pathways for goal-directed limb control
Brain stem tracts
Medial
•Tectospinal (from superior colliculus)
•Reticulospinal (from reticular formation)
•Vestibulospinal (from vestibular nuclei)
Lateral
•Rubrospinal (from magnocellular division of red nucleus)
Cortical tracts
Primary motor cortex; premotor cortical areas
•Lateral corticospinal tract
•Ventral corticospinal tract
Relevant reading: ch. 33 in “Principles”